is bead on a 4 really worth it?

the guitarist in the band i'm trying to form insists on tuning to b w/his 6 string guitar. his seems to sound fine but my basses are 4 strings and i would have to use a 5 string set (minus g) plus do some work on the nut and bridge to make 'em fit. i could do this, but i have 2 fairly expensive basses (a stingray and a corvette) and i really don't feel comfortable making these kinds of modifications. i do understand that the lower tuning is really appropriate for the style of music we play (sludgy doom metal) but wouldn't drop d be enough? i also have my own 7 string guitar for song writing purposes, and i rarely see the need to play below d anyways. it's frustrating to have this kind of disagreement because we otherwise get along great and have identical goals for a band.

Just convert one of the basses... IF that is a direction you end up going. Otherwise, those same notes are found elsewhere on the fretboard....if he insists on playing so low register, then be his foil and play higher and explore the sonic area he's ignoring.